Full array of PHP implementations (recursive algorithm)

Algorithm Description: If p is used to denote the full arrangement of n elements, and Pi means that n elements do not contain the full permutation of element I, (i) pi denotes the arrangement of the prefix I in front of the permutation pi, then the full arrangement of n elements can be defined recursively:
① if n=1, then the permutation p has only one element i;
② if n>1, then the entire arrangement p is composed of the permutation (i) pi;
By definition, you can see that if you have generated the permutation pi for (k-1) elements, then the arrangement of the K elements can be generated by adding element I to each pi.

1.

1<?PHP2 functionRank$base,$temp=NULL)3 {4     $len=strlen($base);5     if($len<= 1)6     {7         Echo $temp.$base.‘ <br/> ';8     }9     ElseTen     { One          for($i= 0;$i<$len; ++$i) A         { -Ranksubstr($base, 0,$i).substr($base,$i+1,$len-$i-1),$temp.$base[$i]); -         } the     } - } -Rank (' 123 ');

However, there is a problem with this algorithm: if there is the same element, then there is a full array of duplicates. For example, there are only three cases of the full arrangement of ' 122 ': ' 122 ', ' 212 ', ' 221 ';

2, the above algorithm based on the price of the re-operation can be

1<?PHP2 functionFsrank ($base,$temp=NULL)3 {4     Static $ret=Array();5     $len=strlen($base);6     if($len<= 1)7     {8         //echo $temp. $base. ' <br/> ';9         $ret[] =$temp.$base;Ten     } One     Else A     { -          for($i= 0;$i<$len; ++$i) -         { the             $had _flag=false; -              for($j= 0;$j<$i; ++$j) -             { -                 if($base[$i] ==$base[$j]) +                 { -                     $had _flag=true; +                      Break; A                 } at             } -             if($had _flag) -             { -                 Continue; -             } -Fsrank (substr($base, 0,$i).substr($base,$i+1,$len-$i-1),$temp.$base[$i]); in         } -     } to     return $ret; + } - Print' <pre> '; the Print_r(Fsrank (' 122 ')); * Print' </pre> '; $?>

Full array of PHP implementations (recursive algorithm)